1. Field of the Invention
The present invention relates generally to oil well equipment and services related thereto, and more particularly but not by way of limitation, to an apparatus and method to insert continuous lengths of small diameter tubing into a live oil well or the like, and for withdrawing the tubing therefrom.
2. Background
It is often advantageous to be able to install a continuous string of tubing into an oil well during development and production, as having such a tubing string installed provides the capability to pump certain types of fluid into the well for various purposes, such as for displacing undesirable fluids within the well, for stimulating production of the well and for cleaning and preventing corrosion of expensive well components. It is preferable that the tubing be inserted while the well remains pressurized to avoid the inherent risk of well casing damage associated with shutting down the well. Furthermore, it is desirable to use injection equipment and methods that minimize disruption to routine production activity.
The benefits of using inserted tubing, however, are accompanied with potentially expensive risks, and these must be minimized. A tube failure, such as tube breakage, kinking or corkscrewing, that occurs in the well can require recovery procedures that can be expensive and time consuming.
Attempts have been made to meet the needs of injecting and removing tubing in the relatively rugged environment of a well site. A device generally known as a coiled tube injector receives continuous lengths of coiled tubing, and a gripping mechanism straightens and delivers the tubing to the well. When it is desirable to remove the tubing from the well, the coiled tube injector works in reverse to withdraw the tubing from the well and pay it back onto a reel for storage. With a coiled tubing injector the same tubing can be reused many times again.
An example of a coiled tube injector is described in U.S. Pat. No. 4,585,061, issued to Lyons, Jr. et al., which illustrates a generally known approach of gripping the tubing and conveying it by a pair of opposed conveyors. The opposed conveyors provide a tube path through which the tubing is moved toward or away from the well bore, depending on the selected rotation of the conveyors.
Although improvements in the art have been made, many shortcomings of present-day coiled tubing injectors are known. One major problem is that the coiled tubing injector cannot be positioned on or removed from a continuous length of tubing without cutting the tubing. Typically, a well servicing contractor inserts the tubing to a specified well depth, and after cutting the tubing, removes the tube injector equipment from the well site. Cutting the tubing is limiting because the injected tubing obviously cannot then be used to inject fluids at a greater depth. Although welding the tubing after cutting is possible, such welding requires specialized skills and cumbersome cleaning and purging procedures. There is a need for an injector that would un-grip the tubing and then could be removed from a medial portion of the continuous tubing, leaving a substantial length of the tubing in place for use at the well site.
Another problem is that existing coiled tubing injectors are large and cumbersome, making it difficult to reach many well sites. For example, the coiled tube injector of U.S. Pat. No. 4,585,061 mentioned hereinabove requires a tractor-trailer rig that is difficult if not impossible to maneuver to many well sites. There is a need for a light weight, self-contained unit that can be transported across difficult terrain and through narrow passageways.
Still another problem is that existing coiled tubing injectors are limited to use with a single size of tubing. There is a need for a unit that accepts multiple sizes of tubing to accommodate different injection needs, depending on the flowrate and the physical properties of the fluid being injected.
The mechanical complexity of existing coiled tubing injectors is a major problem. The need to transfer a gripping force by the rotating conveyors that is sufficient to support and withdraw extremely long lengths of tubing has been met by complicated transfer assemblies made of many complicated and unique components. This results in an expensive manufacture of the apparatus, as well as expensive maintenance and repair for the operator.
There is a need for a low-cost design that simplifies the gripping action and that provides a reliable coil tubing injector requiring low-cost maintenance. These problems are resolved and other unrealized potentials in the art are gained by the present invention.